The present invention relates to combination weighing machines and is concerned in particular with correction of weight signals in such machines by means of historical data derived from the scales.
In combination weighing machines, a plurality of scales receive quantities of a product, and provide an indicated weight signal representative of the weight of product deposited in the scale. Such a weighing machine is shown and described in co-pending application Ser. No. 430,354 filed Sept. 30, 1982 now U.S. Pat. No. 4,466500 by Mosher, Douglas et al. Such machines generally operate in combination with a packaging machine, and the operation of the two machines is synchronized at a high cyclic rate determined either by the packaging machine or the weighing machine. The weighing machine searches for a combination of scales that will most nearly form a charge of product at a desired weight and dumps the selected scales into a single bag or other packaging container within relatively short cycle times.
The desire to improve the production rate of packaging machinery leads to the operation of such machines at a maximum possible rate which is established either by the limitations of the packaging machine or the weighing machine. In the case of the weighing machine, the upper limit of operation is in part determined by the period of time required to drop a quantity of product into a scale and allow the scale to settle out so that a reliable, relatively steady state weight signal can be taken from the scale for conducting the combination search. The dynamic conditions associated with the depositing of the quantity of product in a scale, including the fact that the product acquires momentum as it is dropped, interfere with the weight signal from the scale and, until now, have required that in each cycle of operation, the machine allot a period of time for the scale signals to settle out (settling time).
It is an object of the present invention to improve the rate at which a combination weighing machine operates by reducing the amount of time that is allotted for settling of the weight signal during each cycle of operation. This object is achieved by making corrections to the unsettled weight signals in accordance with a correction parameter that is determined from historical data taken from the scale.